DESCRIPTION: The goal of this project is to characterize the structure and function of the human "classical" reduced folate carrier (RFC). Human cDNAs isolated in the applicant's laboratory restore MTX sensitivity and RFC activity in transport-defective Chinese hamster ovary cells. Studies are proposed to use anti-RFC antisera to examine structural and functional relationships between other folate transport proteins and the RFC, clone the gene for the RFC and map the intron/exon boundaries and promoter region and identify the structural and functional domains of the human RFC.